Fluid therapy or the infusion of physiologic solutions into the blood of patients is a standard treatment for a variety of medical conditions including shock due to blood loss, sepsis, and burn injury. Fluid is often administered from fluid containers such as bags or bottles using mechanical pumps, hand pumps, gravity flow or pressurized sleeves that compress the fluid container. For the treatment of certain medical conditions, it is important for a caregiver to know an amount of fluids that have been administered to a patient and a timing of such fluid administration in order for a response of the patient to the fluids to be gauged, which may inform subsequent treatment activities.
One example of such a treatment is fluid resuscitation of burn shock. Following major burn injuries, the integrity of the blood vessels in the damaged tissue become leaky to fluid and plasma proteins that extravasate into the tissue spaces. This loss of vascular volume results in inadequate perfusion to vital tissues. Therefore, a standard treatment for burn-injured patients is fluid resuscitation whereby a fluid is administered to the patient at a specified rate for a specified duration (e.g., one hour). Because burn patients are at risk of under- and over-resuscitation, which can have harmful effects, it is also common practice to evaluate the patient's response to the administration of fluids (e.g., urinary output and mean arterial pressure) so that the infusion rate of fluids can be adjusted to an appropriate value.
Another example of such a treatment is the administration of fluid boluses, which are relatively large volumes of fluid administered over a short duration to hasten or magnify patient response, for the treatment of hypovolemia (decreased blood volume) and hemodynamic instability (abnormal or unstable blood pressure). Fluid boluses are typically administered at a high infusion rate for a relatively short duration to deliver a prescribed volume, and, perhaps equally as important, to enable the assessment of a patient's responsiveness to the administration of fluid. There are several direct and indirect measures of a patient's fluid responsiveness such as a defined increase in cardiac output. When the patient responds with increased cardiac output or perfusion after a fluid bolus, the caregiver can ascertain that the fluid was of benefit. However, if the patient does not respond adequately, this informs the caregiver that the patient is a non-responder and requires therapeutic measures such as cardiovascular drugs. Although the description below refers generally to intravenous (IV) fluid administration, fluid administration can also take place via interosseous (IO) and intramuscular (IM) routes.
When an IV fluid is administered by gravity feed without an infusion pump, the infusion rate is typically controlled manually by adjusting the clamping pressure on the IV infusion tube (e.g., via an adjustable thumbwheel) that connects the IV fluid container to a patient's venous catheter. To determine the infusion rate using this delivery method, a caregiver typically counts a number of drips over a given time period (e.g., one minute) to calculate and adjust the infusion rate and attempts to verify the infusion rate over a longer time period by observing a change in fluid volume in an IV fluid container, which can be highly inaccurate. When an IV fluid is administered using an infusion pump, the amount of fluid that is delivered is controlled by adjusting the infusion pump's flow setpoint. While infusion pumps allow for a more accurate control of infusion rate, they are expensive and most often fail to deliver fluid at the fast rates needed for a bolus. Because certain treatments require a precise measurement of the amount of fluid delivered and of the timing of fluid delivery, there is a need for a more accurate system and method for measuring these parameters either as a redundant measure to verify the data available from an infusion pump or as an accurate measure of fluid administration in the absence of an infusion pump.
U.S. Pat. No. 8,579,859, which is incorporated herein by reference in its entirety, describes a variety of designs of IV fluid administration systems that incorporate load cells for measuring the weight of an IV fluid bag, the change in which enables the determination of fluid administration parameters. However, the sensitive load cells that enable accurate measurements of the amount of fluid that is being administered are also susceptible to error caused, for example, by movement of the IV fluid bag, which may be exacerbated when fluids are being administered in a moving vehicle such as an ambulance or patient transport air vehicle.
While known filtering techniques significantly remove signal noise, they also reduce temporal resolution of the signal, which can be unacceptable, especially in the provision of fluid boluses in which it is desirable to identify the start and stop times of the high infusion rate period with a high degree of precision. There is therefore a need for a system and method for removing signal noise from a load cell signal for accurately determining fluid administration parameters based on weight measurements of a fluid container. In addition, there is a need for providing these determined fluid delivery parameters in real-time or near real-time and in conjunction with additional patient responsiveness parameters to provide caregivers with improved situational awareness.